The ratings agency said there’s more than a 50 percent chance it would lower the UK’s rating, which determines how cheaply a country can borrow money, in the next two years, Forbes reported.

The reasons for the outlook downgrade? The UK’s indebtedness levels are “significantly above the ‘AAA’ median,” the company said, according to Forbes, and any intensification in Europe’s sovereign debt crisis could limit the UK’s ability to hit its deficit reduction targets. The ratings agency drew attention to the fact that the UK’s structural budget deficit is second in size only to the United States, the Wall Street Journal reported.

"This is a salutary reminder as to why Britain needs to deal with the enormous debts and deficits we inherited, why we have got to stick to [deficit reduction] plans,” Chief Secretary to the UK Treasury Danny Alexander told BBC News. The UK Treasury releases its budget for the year next week.

Last month, Moody's Investors Service also cut its outlook on the UK, the Wall Street Journal reported. Standard & Poor's, the third major ratings agency, maintains its stable ratings outlook for the UK.